1. Field of the Invention
The present invention is directed to a process for removing oxygen from a refractory metal. More particularly, the present invention describes a process for removing oxygen from a refractory metal by treatment with a metallic deoxidant.
2. Background of the Prior Art
It should be understood that the invention concerns a process for the deoxidation of refractory metal and metal alloys which contain only minor amounts of oxygen, as contrasted with processes for the reduction of ores to produce metal. Processes to reduce ores or metal oxides to metal usually require extreme temperatures, as shown in several disclosures. For example, U.S. Pat. No. 2,834,667 to Rostron teaches direct thermal reduction of titanium dioxide by using metallic magnesium at a temperature not substantially less than 1000.degree. C. U.S. Pat. No. 2,537,068 to Lilliendahl et al. shows the reduction of zirconium oxide or double chloride with calcium at temperatures between 1100.degree. C and 1200.degree. C. U.S. Pat. No. 2,653,869 to Gregory et al. which discusses the manufacture of vanadium powder from vanadium trioxide mixed with calcium and calcium chloride at a temperature between 900.degree. C. and 1350.degree. C. U.S. Pat. No. 4,519,837 to Downs describes a method of reducing metal oxide powders at 600.degree. C. using molten lithium and magnesium or molten lithium and calcium metals.
A pure metal or alloy can become contaminated with oxygen by the various cutting, machining, rolling, forging and heating processes used to shape and work the metal. Although processes are known which remove surface oxide scale from metal e.g., washing with detergents, acid pickling, shot blasting and grinding, no practical commercial method has yet been developed to remove oxygen which has diffused into the lattice structure of the metal itself.
The use of calcium to reduce refractory metal oxides, in distinction to the removal of minor concentrations of oxygen, is well known. However, the use of calcium to deoxidize superficially oxidized metal, i.e. minor concentrations of oxygen, has been less successful. Prior art methods require high temperatures and an excess of pure, expensive calcium for this purpose. Generally these methods use multiple reductions or treatments to completely remove oxygen from the final metal. As suggested in the Rostrom '667 patent, calcium could be dispersed in a fused calcium chloride bath, maintained at about 1000.degree. C. or higher, and used to deoxidize titanium scrap metal. However, large excesses of calcium and calcium chloride are required.